Surface miners with a roller-shaped mining member for the selective mining of mineral raw materials occurring in sedimentary beds operate according to various mining methods. They depend essentially on the maneuverability of the miner and its type of mining and its mining performance. The design and the mode of operation of the mining member, the type of the chassis and the arrangement of the mining member in relation to the chassis, as well as the attainable mining performance are therefore very important for the design of such a miner. The mining performance of such a miner is determined by the cutting height, the cutting width and the feed speed. The feed speed is the velocity of travel of the miner. Since the wear of a miner increases in proportion to increasing velocity, it is important to appropriately coordinate the parameters that determine the mining performance with one another. Two possibilities of arranging the roller-shaped mining members in relation to the chassis have been known from the German journal Braunkohle, Surface Mining, 49 (1997), No. 2, pp. 123-128: The central arrangement and the frontal arrangement on the frame of the miner. The central arrangement of the roller-shaped mining members is defined here as their arrangement between the front and rear caterpillar elements (endless belt drive unit)and the front arrangement is defined as their displacement in the direction of travel and mining in front of the chassis. A first embodiment with a central arrangement has been known according to the U.S. prospectus "Easi-Miner.RTM., Model 1224, Continuous Surface Miner" of the firm of Huron, U.S.A., and the patent specifications according to U.S. Pat. No. 4,536,037 and U.S. Pat. No. 4,690,461. The surface miner is equipped with a four-caterpillar chassis, wherein the caterpillar elements arranged in front of the mining member and the caterpillar elements arranged behind it are not steerable. The mining member designed as a milling roller is located between the front and rear caterpillar elements. The loosened material is thrown from the milling roller operating with an undershot onto a discharge belt, it is conveyed further there, and is transferred from this to a loading belt. The front pair of caterpillar elements of the chassis normally moves on the level to be removed, while the rear pair of caterpillar elements moves on the freshly removed level. If the miner operates in parallel next to an already removed block, an individual front caterpillar element of the caterpillar pair moves on the upper level directly next to the edge falling vertically. If greater cutting heights are reached, this may lead to the edge being broken off and to the lowering of the caterpillar element in the case of a loose substrate. In the case of unevennesses on the level to be mined off, which are formed, e.g., due to ditches dug to drain off surface water, travel on a straight plane, which is required for an accurate, selective mining of sedimentary beds, is not possible. The configuration of the miner, with the central arrangement of the milling roller, makes it also possible to perform mining while traveling in a curve due to the reliable and accurate steering. After a block has been mined off from the beginning to the end of the surface of the deposit, the miner is turned again and mining work is performed in the opposite direction. The milling roller cannot perform any mining operation between the rear and front caterpillar elements during this change in direction while traveling in tight curves. A similar surface miner, likewise with a central arrangement of the milling roller, has been known from the patent specification U.S. Pat. No. 5,092,659. Miners built according to this basic principle have also been known with a three-caterpillar chassis with one caterpillar element in front of the mining member and two caterpillar elements behind it (literature source: DE prospectus No. 25-21.01.1288, year 1987, "Wirtgen 2600 SM of the firm of Wirtgen). The advantages and drawbacks of the use of these miners are those described above.
The above-mentioned two surface miners are designed for the mining of relatively thin beds and therefore they must travel at a higher speed in order to reach an effective delivery output. They are therefore particularly suitable for loading the mined material on trucks, whereas they are only conditionally suitable for loading belts via a transfer conveyor. According to patent specifications U.S. Pat. No. 5,092,659, another surface miner with central arrangement of the roller-shaped mining member has been known. The most essential difference from the above-described, prior-art solutions is that mining operation can be performed in two opposite directions of travel due to the symmetrical arrangement of the mining member between the caterpillar groups and the specific design of the milling tools. As a result, turning is not necessary at the end of a block being mined. As a consequence of the steerability of all caterpillar elements of the chassis, the miner has good maneuverability and is also able to perform work while traveling in curves. Shorter runout ramps are sufficient at the end of each block being mined compared with the above-described miners. Since the particular caterpillar group that is in the direction of travel always travels on the upper level to be mined, the same drawbacks arise here as those described above concerning the breaking off of the edge in the direction of the lower-lying soil already mined and in the case of possible unevennesses on this upper level. One specific drawback of this miner is the complicated conveying of the cut material in the horizontal direction from the milling drum. The surface miner can mine the material in relatively thick beds compared with the above-mentioned two miners, it can travel correspondingly slowly, and it is suitable for conveying the mined material to a face conveyor via a transfer conveyor or a conveyor bridge.
All surface miners in which chassis parts are arranged in front of the mining member, as in the above-described three surface miners, also have, in principle, the drawback that they are unable to mine a residual material at the ends of a block being mined. This residual material must therefore be mined in a special operation.
The surface miner with the frontal arrangement of the roller-shaped mining member, which is known from the journal Braunkohle, Surface Mining, 49 (1997), No. 2, pp. 123-128, is equipped with a two-caterpillar chassis. As a result, turning is possible on the spot at the end of a block being mined. Travel in curves of any radius is also possible with this chassis arrangement, but high chain tensions always occur here, because the caterpillar element that is the inner caterpillar element in the curve always exerts a braking force and the caterpillar element that is the outer caterpillar element in the curve must overcome the normal propulsive force and additionally the braking force of the caterpillar element that is the inner caterpillar element in the curve. The arrangement therefore requires a high installed power and the chassis is subject to great wear. The miner is provided behind the mining member with an auxiliary device comprising a scraper blade and a skid in order to level material being conveyed that has been detached but not completely picked up on the roadway and to guarantee the secure position of the miner in the case of increased front-side load during the detachment and picking up of the material being conveyed. As a result, the necessary propulsive force increases. The miner has a relatively great mining height, because it can be in working connection with the material with its pick-up member over up to about two thirds of its diameter; it travels correspondingly slowly and can discharge the material being conveyed onto a face conveyor.